The attack, which happened during the weekend, is the latest in the region as the conflict with Boko Haram nears its ninth year.

“WFP can confirm that a convoy escorted by the Nigerian military including WFP-hired trucks was the subject of an attack by armed groups 35 km southwest of Ngala in Borno State on Saturday,” the spokeswoman Jane Howard said in a statement.

“Four people, including the driver of a WFP-hired truck and a driver’s assistant, were killed in the incident.”

“WFP is working with the authorities to determine the whereabouts of the trucks.”

The spokeswoman declined to comment on whether the driver and assistant were WFP staff, or give details about the other two people killed.

The military has not commented on this latest attack.

Last year, the United Nations suspended aid deliveries in Borno after a humanitarian convoy was attacked, leaving two aid workers injured.